Protective device for transformers.



No. 861,003. PATENTED JULY 23, 1907. E. A. WAGNER.

PROTECTIVE DEVICE FOR TRANSFORMERS.

APPLICATION FILED DEO.18,1906- Fxal- 5 FIGE- Flsfl WITN E55 E5 INVENTUR EDWARD \/\/ABNER.' I gm MQIQ 13g ATT UNITED STATES PATENT OFFICE.

EDWARD A. WAGNER, OF FORT WAYNE, INDIANA, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

PROTECTIVE DEVICE FOR TRANSFORMERS.

Specification of Letters Patent.

Patented July 23, 1907.

Application filed December 18, 1906. Serial No. 348,898.

To all whom it may concern:

Be it known that I, EDWARD A. WAGNER, a citizen of the United States, residing at Fort Wayne, county of Allen, State of Indiana, have invented certain new and useful Improvements in Protective Devices for Transformers, of which the following is a specification.

My invention relates to the protection of transformers and other electrical apparatus employing oil as an insulating medium, and its object is to prevent a burn-out or short-circuit, due to the presence of water which may have found its way into the oil in operation.

It is well known that mineral oils, when freed of moisture, are excellent insulators, and for this reason oil has been commonly used in transformers and other apparatus for insulating purposes. The insulating value, however, falls away rapidly with the introduction of a small quantity of water into the oil, as by sweating of the inside of the casing up to the change in temperature, or in the case of water-cooled transformers, by leakage from the cooling pipes. The presence of .01 of water in mineral oil will lower its value about 50 per cent, and the presence of 1% of water will lower the insulating value about 90 per cent. It is evident from these figures that a sinall proportion of water may lower the insulating value of the oil sufliciently to cause a burn-out of a transformer coil, but the only way that it has been possible heretofore to ascertain whether water is present in the oil, while the transformer is in service, is to draw off a small amount for testing.

I purpose, by my invention, to indicate the lowering of the insulating qualities of the oil, so that steps can be taken to change the oil before damage has been done to the transformer coil. I accomplish this result by submerging a spark-gap in the oil near the bottom of the casing and impressing a voltage on the terminals of the spark-gap. The spark-gap terminals are far enough apart so that when the oil is free"irom water, no current can flow from one terminal to the other; but if Water is introduced intothe oil it settles to the bottom of the casing, reducing the dielectric strength of the oil between the spark-gap terminals, so as to allow a current to jump the spark-gap. This current may be utilized to protect the transformer in any suitable manner.

My invention will best be understood by reference to the accompanying drawing, in which Figure 1 shows an elevation, with the casing in crosssection, of a transformer provided with a protective device, in accordance with my invention; and Figs. 2, 3 and 4 show different sections of the protective circuit.

In Fig. 1, A represents the transformer casing, which contains the laminated core B and the transformer coils 0, carried thereon. The casing is filled with oil to a level above the transformer windings, thereby insulating them from each other and from the core.

D D represent the terminals of a spark-gap which is submerged in oil near the bottom of the casing. These terminals may be connected to any suitable source of voltage. In Fig. 1 they are shown connected in parallel to the primary leads E E. This connection is also shown in Fig. 2, in which C represents the primary and G the secondary of the transformer. The spark-gap D is connected directly in parallel with the primary. When the dielectric strength of the oil at the bottom of the casing is lowered sufliciently to permit the current to jump the gap, this current may be utilized to blow a fuse F or to trip a circuit breaker in series with the transformer primary.

In place of relying on the current-flow across the spark-gap to actuate an overload protective device in the main circuit of the transformer, the arrangement shown in Fig. 3 may be used. In this figure, a protective device G is inserted in series with the sparkgap and suitably protected by a resistance H. A flow of current across the spark-gap terminals will energize the protective device G, which may be either an indicating device, such as a lamp to give warning to an attendant, or a magnet coil controlling the transformer circuits.

Instead of impressing the main transformer voltage on the spark-gap, an auxiliary source of voltage, such as the small transformer I, may be employed. This last arrangement is particularly suited for transformers of high voltage, or transformers which are supplied from circuits of high current capacity.

Many other suitable arrangements will be obvious to those skilled in the art.

Further, although I have illustrated my invention as applied to the protection of a transformer, it is obviously equally applicable to other oil-insulated electrical apparatus.

Accordingly, I do not desire to limit myself to the particular construction and arrangements of parts here shown, but aim in the appended claims to cover all modifications which are within the scope of my invention.

I What I claim as new and desire to secure by Letters Patent of the United States, is,

1. In oil-insulated electrical apparatus, in combination with the inclosing casing, a spark-gap submerged in the oil near the bottom of the casing and connected to a source of voltage.

2. In oil-insu1ated electrical apparatus, in combination with the inclosing casing, a protective circuit comprising n aom'ee of voltage and rt spark-grip connected thereto and nulmtergetl tn the 011 near the bottom of the casing.

it. in oil-insulated electrical uppm'ntus, in combination with an tnclosing casing, a. sparkrap submerged in the oil near the bottom of the casing and connected to a source of voltage, and a protective device in series with said sparkgap.

4. In oil-insulated electrical apparatus, in combination with an inclosing casing, a protective circuit having expound tevmhmin nhbmevged hi the oil adjacent each other 10 none the bottom 01' the casing.

In witness whereof, I have hereunto not my hand this Tth day of December, 1906.

EDWARD A. WAGNER.

Witnesees JAMES J. W000, W. H. CRIGHTON. 

